Electrical musical instrument



Dec. 27, 1938.

F. TRAUTWEIN I ELECTRICAL MUSICAL INSTRUMENT Filed March 28, 1936 SShQEtS-STIGEL l Dec. 27 1938. vr-' 'TRAUTWEIN 7 2,141,231

ELECTRICAL MUSICALIQNSTRUMENT Filed Mgrch 28, 1936 3 Sheets-Sheet 2 Patented Dec. 27; 1938 curren STATES ELECTRICAL MUSICAL INSTRUMENT Friedrich Trautwein, Berlin-Zehlendorf, Germany Application March 28, 1936, Serial-N0. 71,397

in Germany March 24, 1930 1? Claims.

application is a continuation in part of application Ser. No. 542,400 filed June 5, 1931, now Patent No. 2939201.

The present invention relates to electrical musical instruments in which electrical oscillations are produced by electrical discharge de vices and converted into sound by loudspeakers. The electrical oscillations are so influenced by a play board that the frequency of the sound, the sound intensity, the timbre and the char-- acteristic of the acoustical oscillations at the start, at the end and during changes of the sound which are h reinafter called transitients are adjustable.

According to the invention, the electrical mu sical instrument is provided with one or more generators producing dam ed oscillations of a frequency in audible range these generators be-= :ing hereinafter called first generators and one 20 or more further generators producing undamped electrical oscillations of a frequency in audible range, these generators hereinafter being called second generators. The first generator or generators are so electrically coupled to the second 25 generator or generators that oscillations started in the first generators in regular sequence of a frequency corresponding to the oscillation frequency of .the second'g'enerators.

lhe first generators may be designed accord- 3 ing to a feature of the present invention as band-pass filters. In another form, the

generators are mechanical oscillators the oscil lations of which are converted into electrical oscillations by microphones, magnetic or electric a induction or like means. The oscillations of the first generators may be translated or transferred by the aid of electrical filters.

If a plurality of first generators are combined with a single second generator, the first genera- 40 tors according to a feature of this invention may be connected to each other by an adjust= able resistance by which the proportion of the amplitudes of the oscillations of the first generators may be regulated.

45 The adjustable resistance may be in the form of a pedal or another device which can be operated independently of the playing by hand on the key-board,

In a preferred form of the invention, the fre- 5c quency of the first generators can be periodically changed with a periodicity in the order of about 3 to 30 changes per second.

The second generators may be electric discharge devices, preferably gas discharge tubes of the kind producing saw tooth: voltage Waveforms, as used in cathode ray television systems for scanning an image. Devices of this kind are known in the art as thyratron gas filled relays or grid controlled rectifiers, which, in most forms, are essentially three-electrode thermionic valves, 5 with the addition of a little mercury vapour. To produce saw tooth oscillations, a condenser is connected across the thyratron. The condenser may be in series with a saturated diode, which, thereforapasses a constant current. The to voltage across the condenser builds up at a constant rate, thus giving the uniform velocity stroke of the saw-tooth. continues until the voltage across the condenser is large enough to cause the thyratron to strike. The condenser then discharges quickly through the thyratron and gives a rapid fly back. Devices of this kind are described for instance in Wireless World September 20, 1935, on pages 334:.and 335. The oscillations thereby produced are hereinafter so called relaxation oscillations for the purpose of this specification.

The frequency of these relaxation oscillations will define the pitch of the tone. ihis frequency may be controlled regulating the voltage he- 25 tween the heated cathode and the control electrode which may be located between the cathode and the anode. By a source of current, additional bias is produced in the same circuit so much displacing the working point into the g0 curved portion or the characteristic curve of the generator that the produced musical inter vals are proportional to the adjusted in ervals of the adjustable voltage.

By arranging a condenser of suitable size be- 35 tween the control electrode and the cathode oi the discharge tube it is possible to retard the speed of changes of the voltage in a manner as desired to produce certain musical effects.

The frequency'oi the generator producing the 4G electrical oscillations may be regulated by an adjustable resistance of a linear form, formed by a stretched resistance wire or better by a stretched insulating core on which the resistance wire is spirally wound up with varying or variable pitch of spiral.

For producing two or more independent sounds in a common instrument, two or more of such linear resistance elements may be arranged in parallel to each other and to a common contact 59 bar. In case of two resistance elements the resistances are so connected that the efiective resistance is resulting between the respective contact point and the left end of one of the resistance elements and the respective contact 435 point and the right end of the other resistance element.

The coupling between the generator for producing electrical oscillations defining the pitch of tone and the discharge device for producing the relaxation oscillations may be of such kind as to keep the relaxation oscillations in a subharmonic frequency proportion to the frequency of the generator, in other words, to cause the a discharge device to oscillate with a frequency being a subharmonic fraction of the frequency of the generator. The generator and the discharge device may be formed by a tube of the same kind, in which the oscillating frequency depends on the voltage of the control electrode of each of these tubes and these two voltages defining the frequency may be adjusted by one common regulator.

The adjustment of sound intensity and the starting of the sound are effected by two separate devices which are operated independently from each other. Electrical musical instruments in which a volume controlling device is combined with the play board and actuated by pressing on the play board are known in the art. Experience has shown, however, that this is disadvantageous in instruments with a continuous formation of the pitch of tone as it is extremely diflicult for the player to combine e. g. the musical forms of expression vibrato, glissando and portamento requiring a steady increasing or decreasing of the pitch of the tone with the volume control. Therefore, according to an important feature of this invention, the general or ground adjustment of sound intensity is effected by a separate volume controlling member which may be actuated by other means than the player's fingers, such as a pedal, a knee lever, a mouth piece operated by the blowing pressure, the jaws or the tong or by similar suitable means. Mouth-operated devices will offer the advantage of minimum physiological retardation in respect of the synchronous operations with the play of the fingers. The starting contact, on the contrary, will serve for giving the desired accent to the start of tone by hard or smooth touch for obtaining sforzato effects and the like and for avoiding the cracks otherwise resulting when connecting a loudspeaker to a source of audible current. This separation of the two functions, that is to say, the starting of the sound on the one hand and the adjusting of its final intensity on the other hand by means of two separate control devices and operating means therefor is a very important feature of the invention, by which the playing of the instrument is very much facilitated and the range of artistic possibilities considerably extended.

The electrical oscillations should be formed prior to their application to the loudspeaker. Therefore, the starting contact is so arranged mechanically and electrically as to first produce the contact regulating the kind and frequency of electrical oscillations and then to start the tone that is to say to cause the passage of these oscillations to the sound reproducer after they have been formed.

In order to further avoid cracks in playing, a permanent oscillation of a medium frequency may be automatically produced when no tone is touched this permanent oscillation, however, not being reproduced by the loudspeaker.

For producing fading-out tones such as produced in a piano, an instantaneous switch may be mechanically coupled to the starting contact, this switch causing connection to the generators for a short instance only and actuating a retardation device which causes the amplification to slowly fade out.

In order to produce room acoustic effects, reverberation effects, echo or the like the electrical oscillations may be reproduced and simultaneously recorded and once more or several times reproduced fron the record after one or several short retardirg intervals. Magnetic recording systems are particularly suitable for this purpose as they can be operated with an endless steel belt or wire which is periodically passed along the recorder, a reproducing device, a quenching device, and again along the recorder and so on.

In order to play any desired plurality of sounds simultaneously it is necessary to provide automatic devices by which each of several simultaneously operated keys is connected to one sound generator only. The number of sound generators required in this case corresponds to-the maximum number of voices to be played simultaneously, each of these sound generators covering the whole tone range. The same problem exists in the automatic telephone plants in which only a limited number of main selectors is provided for a large number of telephone lines. Each telephone line possesses one pre-selector which selects a free main-selector. In case of the polyphonic electrical musical instrument the keys correspond to the telephone lines, the main selectors to the sound generating systems. The automatic selective system may be arranged in the manner of the pro-selectors. The selection may be carried out after a local or a temporal principle. In case of the local principle the highest of several'presseddown keys is connected to the first, the next lower to the second sound generator etc. In case of the temporal principle the key which is first operated is connected to the first sound generator, the secondly operated to the second etc. The temporal principle is superior to the local principle for most requirements, as it permits the player by unnoticeably small temporal differences in operating the keys to connect any key with any sound generator. By assigning a difierent timbre to each of the sound generators a play may be obtained the timbre of each voice of which is a different one.

It may be useful to provide a key board for playing the normal intervals and additionally a linear flexible play band which renders it possible to play any intermediate tones between the keytones or to continuously advance the pitch of tone after the manner of "glissandd or the like.

The middle of each key may be mechanically connected to the corresponding point of the play band so that key board and play band are mechanically coupled and acting together.

Further objects and particulars will be obvious from the following detailed description of some exemplifications of the invention in connection with the accompanying drawings, in which:

Figure 1 is a circuit diagram for a musical instrument embodying the features of the invention,

Figure 2 is a detail partial circuit showing a modification of the invention,

Figure 3 is a partial diagram showing another modification,

Figure 4 is a perspective view of a special keyboard for electrical musical instruments according to the invention,

Figure5 is a partial cross sectional view of Fig. 4.

Figure 6 is a diagram of an automatic relay device for polyphonic playing on an instrument with a limited number of sound generators,

Figures? and 8 illustrate modifications 01' a playing chord or string for use in a system according to Figure 1.

In Figure 1, item 1 is an electric discharge device such as a gas tube, which is shown in hatched manner in distinction from high vacuum tubes. This tube serves for producing relaxation oscillations, the frequency of which is defined by the condensers B and I, the resistance 8, the voltage of the electric source 9, and by the difference between striking and extinguishing voltage of the discharge device i. It is advantageous to make the striking and extinguishing voltage adjust-.

able by means of the cathode 2 heated from the source of current and a control electrode 3. Heating the cathode reduces the extinguishing voltage, while the striking voltage is a function of the voltage at the control electrode 3. Item t is the anode of the discharge device, and item is the heating filament which. is insulated from the cathode.

The elements just mentioned for defining the frequency are available in the instrument for forming the pitch of the sound. ,The oscillating irequencyis controlled by the voltage at the control electrode 3 by subdividing the voltage of the current source 82 through the resistances it, i l with the movable contact devices H and it and the resistance 95. The resistance i5 belongs to the play board. It may consist, for instance, of a wire of 2 or 3 feet length, stretched above a metal strip or rail it between the points it and ill insulated therefrom similar to a onestringed instrument lrnown as a monochord.

lfhrough the earth connection it the metal bar it is connected to the battery it. By this arrangement the oscillating frequency becomes a function of the length same as in chord or string instruments, that is to say the distance between a point to which the finger of the player is applied the point it. Similar to string instruirients pressing down of the wire between the points i! does not influence the frequency. The o of acoustic frequencies available on the play-resistance 25 may be adjusted by the control device ii of the resistance it. The adjustahle contact ii at the resistance i i constructed as a voltage divider defines the working point on the characteristic of the tube i. Thus the working point may be arranged within the curved part of the characteristic of the valve in such a way that the oscillating frequency fairly accurately becomes a logarithmic function of the play wire length so that the distribution of the musical intervals on the play wire becomes proportional to the pitch or the tone. In this case the distance between the notes is the same in all acoustic frequency ranges without becoming smaller as in string instruments. If desired, however, the player may adjust other distributions or" intervals with the aid of the resistances l3 and it, that is to say with smaller tone distances towards the higher notes similar to string instruments.

According to Figure 7 the distribution or intervals may alternatively or additionally be determined by providing a resistance element it having a non-proportional longitudinal rating of the resistance value in such a way that the desired characteristic or distribution of intervals is obtained. According to Figure 8 this may be realized for instance by spirally winding up a resistance wire it on an insulating rope or band 200 and adapting the pitch of the windings to the desired linear resistance characteristic. The wire may be so loosely wound around the rope that the pitch may be subsequently changed, in such a way, however, that the windings are not displaced by the playing.

The relaxation oscillations are transferred to resonance devices 25 and 26 capable of carrying out self-oscillations through a coupling member which according to Figure 1 consists of a resistance 23 and the condenser 24, over transformers 21 and 28. According to Figure 1 these resonance devices consist of electric oscillatory circuits. The inductances of the oscillatory circuits are represented by the transformer secondaries 2'! and 28, shunted by adjustable capacities 3!! and 3!, respectively. The coupling members 23, 24 should be so dimensioned that in each period of the relaxation oscillation a short current impulse is transferred only which has a shock-like character similar to the current passing through the electric discharge device i. The oscillatory circuits 25, 26 accordingly become generators of damped oscillations. They are hereinafter termed first generators. Their frequency defines the timbre of the tone. The electric discharge device i together with the resistance 8, capacity it and l and source of current 5 are hereinafter termed second generator, with its frequency defining the pitch of the sound. The adjustable resistance 29 serves for controlling the mutual amplitude proportion of the damped oscillations in the circuits and 25. According to the position of its operating lever 22 it acts as a shunt to either of the two transformer primaries 2i or 23. If tuning one of the circuits 25 and it to a high and the other to a low frequency, it is possible to gradually change over from bright to hollow frequencies.

The operating lever 22 may be independently operated, for instance foot-operated, so as to render it possible to easily change the timbre during the play. The frequencies of the first generators should preferably be chosen higher than those of the second oscillator, the first and second frequency being perfectly independent from each other and independently adjustable. Even if a first frequency is higher than a second one, the

timbre is changed because the starting-, fadingand change-over phenomena or transitients cause an impression of a certain timbre in the ear.

The oscillatory circuits and 26 are connected to an amplifier tube 33 over a condenser 38. with a grid-deals resistance 35,, in the manner known from the amplifier art. The negative bias of the grid 32 of the valve is produced by the resistance 39. The plate voltage may he obtained from the source of current 9 through the anode resistance 3?. Tide source of current 5" of the valve 33 may be identical to the source of current 5 of the valve 1 for heating its cathode, provided that the cathodes and 2" are indirectly heated as shown. The valve 533 in this case acts as a pro-amplifier, followed in the example shown by the main amplifier 39 and the loud speaker it. The control of sound intensity and the tone starting is effected between the pro-amplifier and main amplifier. Connected to the coupling condenser 323 are the starting contact ill-and the resistance ll controlling the sound intensity. The lever 52 of the resistance ll may be in the form of a pedal as indicated in Fig. l. The starting contact iii merely serves for smoothly connecting and disconnecting the sound generators to the sound reproducers to prevent the cracks which are normally produced when conmeeting or disconnecting audio frequency currents to a sound reproducer by metallic contacts. The contact device which hereinafter is called starting contact 40 therefore consists of a resistance material the contact resistance of which is a function of the pressure applied thereto, such as carbon or a cloth impregnated with a conductive liquid, such as glycerine, arranged between two metal surfaces. By means of the resilient buffers 43 and 44 the starting resistance 40 is so arranged under the bar [8 that its resistance is infinitely large in state of rest and therefore no audio current is applied to the main amplifier 39. By pressing down the wire I5 against the bar l8, the resistance of the starting contact 40 steadily decreases to its minimum. The starting device is so provided that the minimum resistance and with it the final sound intensity is reached with a small actuating pressure so that the sound intensity proper is not influenced and cannot be controlled by this starting device. This is effected by suitably proportioning the resistances 4| (volume control) and 40 (starting contact). For instance, if the, adjustable resistance 4| has 10,000 ohms in its middle position, the starting resistance 40 should be so provided to reach its final value of some hundred ohms (up to 10% of the resistance 4|) at an actuating pressure of Shot sounds similar to those occurring when suddenly switching in audible currents may likewise result when suddenly changing over from one frequency to another if the starting contact remains pressed down between the two notes. To make such changes smooth, a condenser 45 is connected in parallel between control electrode 3 and cathode 2 of the electric discharge tube this condenser being so dimensioned in respect of a middle position of the resistance I5 that the transition from one frequency to another goes smoothly and yet so quickly that it is not disagreeably noticed from a musical point of view. A further means for avoiding shot or crack noises is the permanent oscillation. Through a switch 46 and an adjustable resistance 41 an electric source 48 is connected to the point IT in Figure 1, this electric source closing the circuit of the electric source I2 over resistances 3, l4 and I5 even if the contact I9 is open and no key depressed so that a frequency is resulting which is accurately adjustable by the resistance 41. The starting contact 40 being open if no pressure is exerted to the play board this audio frequency current is not imparted to the main amplifier and loudspeaker. The permanent oscillation further serves for permanently keeping the electric source i2 to an average load so that its voltage and accordingly the tuning of the instrument is varied as little as possible.

In Figure 1, filter circuits are inserted between I additionally controlled. With the aid of the However, timbres such ascircuits by inserting variable condensers 30 and 3 I connected in parallel to the primary zindings of the transformers 21 and 28. However, it is important that damped oscillations of definite frequencies are produced by these band-pass-fllters. The band pass filter offers an advantage over the simple resonance circuit in so far as that damped frequency of its passage range is produced therein which is harmonic to the frequency of the second generator, or in other words in case of a variable second frequency a band-pass filter automatically oscillates with the best efllciency.

Instead of electrical circuits the generators 25 and 26 may comprise mechanically oscillating structures such as metallic tongs, or equivalent means such as strings, cords, plates, cavities or hollow spaces (not shown) and the like which are energized from the second generator by electromagnetical devices and the oscillations of which are converted into electrical oscillations by means of microphones or the like.

A device of this kind is shown in Figure 2. The coupling member 23, 24 forms the connection to the identically designated parts of Figure 1. The oscillatory circuits 25 and 26 with their auxiliary devices 27 to 3| are replaced by the resonant tong of iron 53 which is tightly clamped at 54. It is excited by the electromagnet 55. Its oscillations are received by the magnetic pick-up or pick-up 56 and impressed upon the pre-amplifier tube 33 applied in the same manner as described in Figure 1.

Through simple additional devices the electrical musical instrument according to the invention produces musical effects such as mechanical tremolo, fading out and reverberated sounds. It has been suggested, already, to produce a mechanical tremolo in respect of sound intensity and frequency by periodically varying a member for volume control or a frequency controlling member respectively. Figure 1 shows how such a tremolo of the frequency may be produced. A condenser 1 comprising the electrodes 51 and 58 may be shunted to the condenser 5 through the switch 59. The electrode 53 of this condenser 1 can be rotated by the motor 60 with a speed of up to 30 revolutions per second. By rotation of the condenser the frequency produced by valve is modulated in the rhythm of the rotation of the condenser 1 due to the change of the relaxation frequency produced by the consequent change of the capacity of condenser 1. Hitherto, it was unknown that a rapid tremolo with a frequency at the lower audible limit (about 16 to 30 revolutions of the motor per second) produces the impression of several instruments playing simultaneously.

Also it was so far unknown in electrical musical instruments to form a tremolo of the timbre for instance by connecting over a switch 65 a rotating condenser 6| with the electrodes 62 and 53 and the motor 64 in parallel to the condenser II. The rapid tremolo of the timbre likewise produces the effect of several instruments, while the slow tremolo of the timbre produces an attractive musical efi'ect.

Fading-out sounds are produced by reducing the amplification after the start of the tone with the desired speed. For example, according to Figure 1 this is effected by separating the anode voltage from the valve 33 by the condenser 66.

For playing-without fading the condenser may be overbridged by a switch 61, if this is at the position shown in full lines in Figure 1. The fading device consists 01' the instantaneous switch of the contact point H and the cathode 2 of 68. If fading out sounds are to be produced the instantaneous switch 68 is changed from one to the other position shown in dotted lines. During this movement the condenser 68 is short-circuited for a moment that is to say in the middle position of the switch shown in full lines, whereby the valve 33 immediately gets the full anode voltage. Due to the opening of the instantaneous switch 68 occurring shortly thereafter the condenser is discharged in a period depending onits capacity. The fading time can be changed by adjusting the condenser 66 such as by connecting furthercondensers 70 in parallel thereto by means of the switch 69. The instantaneous switch $8 may be mechanically coupled with the starting contact 40 so that by each pressure on the playing device i5, is an attenuating sound is resulting.

The reverberation sound is formed by an extended duration of sound. It may be produced e. g. by recording the sound on a phonographic carrier and repeated acoustical reproduction following in a short interval or intervals. In Figure l the phonographic carrier consists of the endless steel wire H which runs over the two rollers 12 and 73. Parallel to the loudspeaker i is a recording magnet it. The audio current received in the reproducing magnets it, H and i8 is applied to the input of the amplifier 39 over the volume controlling device It. Distance and number of the reproducing magnets 1Eii8 as well as the number of revolutions of the steel band or wire it may be adjustable for controlling the volume and character of the reverberation or echo. Item '14 is a quenching magnet to erase the magnetic records after application to the pick-up device "M in a known manner to enable continuous recording and reproduction. Thus, for instance, room-acoustic effects or the pedal effects of the piano may be imitated.

Inorder to produce several tones simultaneously on the instrument, several devices according to Figure 1 may beoperated in parallel combination, as shown in Figures 4 and 5 wherein the common contact element is provided in the form of a metallic coating 20! applied to the underside of afiexible playing band I16 arranged above playing wires as will be further described hereafter. In order to facilitate the playing, keys may be arranged above the play. wires. Due to the fact that each key depresses all play wires simultaneously, means have to be provided for causing each of several simultaneously depressed keys to make their contact l9 effective to one of the devices only. This is easily possible if two sound generators only are to be combined to a common instrument.

According to the circuit diagram Figure 1 only the distance l9l6 defines the pitch of the tone. Now, it is easily possible to modify the circuit in such a way that the distance iii-i? defines the pitch of the tone, in other words that out of several points being pressed down the lowest only" defines the pitch of tone, while in the circuit ac= cording to Figure 1 the highest depressed point defines the pitch of tone. Figure 3 represents a circuit diagram therefor. The parts which are identical to Figure 1 are designated by the same reference numbers. As will be seen, the diagram Figure 3 results from the diagram Figure 1 by merely interchanging connections and different adjustment of the resistance values. The resistance I 4 is connected to point I! instead of point IS, the control electrode 3 is connected to they negative pole of the current source 12 ins ad the electric discharge device I is connected to the contact ll of the resistance i4 instead of to ground It! as in Figure 1. The devices 46, 41, 43 for the permanent oscillation are connected to point l6 instead to point IT. The permanent oscillation device is of particular importance in this case because without it a high frequency would result while in thediagram Figure 1 a low frequency or no frequency at all would result if the permanent oscillation device would be missing.

A key-board suitable for playing several tones simultaneously is shown in Figure 4. The resistance wires I5a and I52) are stretched in the same way as shown in Figure 1 with reference to resistance wire I5 between two fixed points not shown in Figure 4. These resistance wires are each inserted in an electrical circuit in the same way as resistance wire it (Figure l) is inserted in the electrical circuit shown in Figure l and are situated below a contact band Hill which is likewise freely stretched and may consist of leather hav ing its underside provided with a metal coating 2M which corresponds to the bar it of figure l and is connected to earth. In order to facilitate the playing so that the chromatic tones are easily and safely hit while continuous changes or the tone pitch (vibrato, glissando, portamento) are also possible, the linear play board is combined with a key board consisting of white keys il and black keys M8. The play band in this case is preferably arranged directly before the black keys as shown in Figure 4, thus facilitating the change-over by the player from the key board to the play band and reversely. The keys may i be coupled to the band by thin rods W9 each of which may be rigidly connected to one key on the one hand and to the respective point of the leather belt on the other hand. The rods We are indicated in Figure by dotted lines and may be fixed under or in the leather belt in a manner similar to that shown in detail in Fig. 5. According to this construction the appertaining keys are pressed down even when playing on the play band.

For instance, if one depresses the band at a point on the boundary line of two adjacent keys, a tone will be produced the pitch of which is between two serni-tones, that is to say the tone forms a quarter-tone interval with respect to the two adjacent semi-tone keys. When so depressing the band, the two adjacent semi--tone keys will decrease by a certain amount; however, the two keys will in this case be moved downwards less than in case of being directly depressed. The band Ht in each case causes the keys immediately adjacent to the depressed key or point of the band to follow the depressing movement to a certain extent so that it is possible to play smoothly glissando" on the band without a hole being formed on the depressed point by the two adia cent non-depressed keys as would occur in case the adjacent keys would not yield to a certain extent. I

By providing a two-tone play device icr either hand a four-tone arrangement can be formed.

A certain kind of polyphonic effect is obtained by deriving harmonic frequencies from a frequency with the aid of synchronization. I have found that for the purposes of my present invention the synchronization of relaxation oscillations is very useful. In Figure 1 a diagram of such a synchronization is represented. The corresponding elements for producing the synchronized oscillations are designated with like primed reference numerals. The control electrode 3' or the synchronized electric discharge device I- is connected to the same point II as the control electrode 3 of the discharge device I and accordingly receives the same control potential as the device I. The cathode 2 is connected to earth same as the cathode 2. The cathode may be heated from a source of current 5' which may be identical with the source of current 5. The discharge tube I' has associated therewith a condenser 6' and a plate resistance 8 which can be regulated. The anode voltage 9 may be common to both electric discharge devices I and I. For the purpose of synchronization a small partial voltage is transferred from the anode 4 of the discharge tube I over the high resistance and the small condenser 8I to the control electrode 3. Due to the resistances 82 and 83 a small fraction of this voltage only will afiect the own control electrode 3 of the discharge device I. With the aid of the coupling members 23' and 24 the synchronized oscillation and the synchronizing oscillations are both impressed upon the further elements of the circuit (amplifier etc.) the synchronized oscillations may be provided with their own generators. amplifiers and loudspeakers as well. In order to adjust the intensity of the synchronized oscillations the resistance 23' may be adjustable. The synchronized oscillator may form a constructional unit with the synchronizing oscillator. It is put in or out of working order by switching in or cutting out the plate voltage by means of the switch 84.

By this synchronization according to Figure 1 subharmonics are produced the ordinal number of which may be controlled by the resistance 8. If the electric discharge devices I and I have approximately the same characteristics the ordinal number remains the same over a wide frequency range.

Figure 6 shows an exemplification of a diagram of an automatic device for connecting three sound generators with the'key board after the temporal principle. The example will make clear the principle after which such devices may be built up for more than three sound generators as well. The relay device per se is working after the wellknown principle of automatic telephone exchanges. The diagram illustrates the application of this principle to an electrical musical instrument according to this invention, omitting the particulars of the relay system which are selfexplanatory from the automatic telephone art. Items 9|, 92 and 93 are horizontally arranged bars the width of which corresponds to the width of one key. Each of these bars is so coupled with the associate key 85 arranged to swing around the axis 86, by means of a rod 89 that the bar moves upwards in the direction and with the stroke as indicated by the arrow I89 relative to the rod 89 (when depressing the key 85). The corresponding keys associated with the bars 92 and 93 have not been shown for the sake of simplicity, but function in the same manner as ke 85 as is understood. Only the upper parts of the rods 90 and I00 have been indicated. In order that the bars 9|, 92 and 93 move upwards parallelly to their initial position when depressing the appertaining key, the guiding members 94, 95, 96, 91, 98 and 99 have been provided. Figure 6 shows a partial view of three successively arranged keys in a device according to the invention. The bars 9|, 92 and 93, which really are situated side by side same as the keys, have been shown arranged below each other in order to give a more distinct illustration. The other keys of the key board are provided with devices of the same kind. Fixed below the bars 9|, 92 and 93' are bored iron plates IOI, I02 and I03, I04, I05 and I06 or I01, I08 and I09 respectively. Movable electro-magnets IIO to H8 are arranged below each iron plate. The construction of the magnets will be seen from the magnet I I I, shown in section. The hatched body is a pot shaped or inverted cup shaped magnet. The ends of the winding are lead to contact terminals at the lower side of the magnet. If such a magnet is fed with current, it will stick to the opposite iron plate and is lifted with the bars 9I, 92 or 93, when lifting the latter, thus effecting the necessary switching. As long as no key is depressed, only the magnet line group H0, H3. H6 is energized from the battery 81 each through the series-connected lower pair of springs of the switch II9, I20, I2I through the associated electro-magnets to the earth I9 through the lower contact of the switches I22, I23 and I24. It has been assumed, in this case, that the medium key is depressed first. The magnet II3 with the bar 92 is thereby lifted and the lower part of the switch I20 cut out. Thus none of the lower magnets, for example IIS can be lifted in the same line group, for the whole line group is now without current. If the player would have depressed two keys at accurately the same time, only the highest would cause lifting of the electromagnet, the successive one being cut off by the switch I20. Accordingly in this device the local principle is used additionally in the case that several keys are depressed at accurately the same time. Through the switches I20 and I34 the magnet H3 is directly connected to the plus pole 88 of the battery 81 on the one hand and to the earth I0 on the other hand, with the aid of the contacts arranged above. The magnet II3 accordingly independently from all other actions occurring thereafter sticks to the bar 92 as long as this is lifted. By lifting the magnet II3 the medium magnet line group III, H4, III has been connected to earth and accordingly is fed with current by the medium spring of the switch I23.

In the same way this line group would have been fed with current if another key would have been depressed. Accordingly after touching one key the following line group is prepared for switching. The magnet line group III, H4, H1 is likewise fitted with switches I25 to I21 and I28 to I30. In the diagram Figure 6 it has been assumed that the lower key is depressed after the medium one. Thus, in the analogue way as the action of magnet I I3 has been described the position of magnet I I I as shown in the drawings is resulting. Now, through the medium spring of the switch I30 the last line group H2, H5, H8 has been fed with current. The case that a third key is depressed, is not shown in Figure 6. It will be clear how the switches I3I to I33 and I34 to I39 would work when a corresponding key would be depressed in the third place. In the last line group, no medium springs are necessary at the switches I34 to I36. If there would exist more than three sound generators, medium springs would be required for feeding the next group. In the last line group the optical or local principle has been so applied that the lowest note is preferred by arranging the contacts I3I to I33 in the order from low to high pitch and accordingly connecting the plus pole 88 of the battery to the lower end of the line group, while the contacts I22 to I24 and I28 to I30 are connected in the order from high to low pitch and the plus 2,141,csi

pole of this line group is connected at the high side accordingly, Rods I31 to I45 are connected with two electro--magnets H0 to H8, said rods extending through bores I46 to I54 in the bars 9| to 93 and hearing at the top elastical caps I55 to I63 acting as artificial fingers. These artificial fingers will produce contact on the resistance wires l5, l5" and W with the contact bars l8, l8" and I8', belonging to three sound generators in the manner shown in Fig. 1. The wires l5, l5" and !5' and contact bars I8, l8" and l8', although really going through, have been represented in three sections, because the bars ill, 92 and 93 have been represented below each other instead of their real position side by side.

1'. In an electrical musical instrument, a resonator capable of generating damped electrical oscillations of a frequency in audible range, a generator producing undamped electrical oscillations of a frequency in audible range, means for exciting said resonator in regular sequence by said generator to produce successive trains of damped natural oscillations of said resonator at the frequency or" said generator, said resonator being capable of oscillating within an extended band of frequencies.

2. In an electrical musical instrument, a resonator capable of generating damped electrical oscillations of a frequency in audible range, a generator producing undamped electrical oscillations of a frequency in audible range, means to excite said resonator in regular sequence by said generator to produce successive damped oscillation trains of said resonator at the frequency of said generator, said resonator comprising a mechanical oscillation device, and means for trans forming the mechanical oscillations of said de vice into corresponding electrical variations.

3. In an electrical musical instrument, a resonator capable of generating damped electrical oscillations of a frequency within the range of audibility, a generator producing undamped electrical oscillations of a frequency within the range of audibility, means to excite said resonator in regular sequence by said generator to produce successlvedamped oscillation trains at the fre quency of said generator, 9, sound reproducing device, and means including an electric filter for transmitting said electrical oscillations produced by said resonator to said reproducing device.

4. in an electrical musical instrument, a pin-- rality of difierently tuned electrical resonators adapted to generate damped electrical oscillations having frequencies within the audible range, a generator producing undamped oscillations of a frequency in audible range, means to excite said resonators in regular sequence by said generator to produce successive damped natural 05 cillation trains of said resonators at the frequency of said generator, and adjustable impedance means for controlling the relative intensity of the oscillation amplitudes of said resonators.

5. In an electrical musical instrument, an electr o resonator adapted to produce damped osclllations or" a frequency in audible range, a gen erator producing undamped oscillations of a fre- -quency in audible range, means for exciting said resonator in regular sequence by said generator to produce successive damped natural oscillation trains of said resonator at the frequency of said generator, and means for periodically varying the natural frequency of said resonator at a rate of the order of up to 30 cycles per second.

6. In an electrical musical instrument, generresponding values of said regulators determining predetermined fixed tones of said generators, and a selective system associated with said key-board, said selective system comprising first contact means associated with each key of said key-board and adapted to connect a depressed key with one of said regulators, a second contact means asso c ated with each key of said key-board and adapted to separate all the non-pressed keys from. the regulator connected with the first mentioned dc pressed key, and a third contact means associated with each key of said key-board adapted to prepare the connection of a successive regulator with all, the non-pressed keys, thereby to enable a successively depressed key to be connected with said second regulator while simultaneously sepa rating the remaining non-pressed keys from said second regulator, whereby several keys producing d fferent tones may be depressed simultaneously without interference between said generators, the order according to which said regulators are connected to the keys being determined by the term 'poral sequence of depressing the keys.

8. In an electrical musical instrument, an eleo=- tric resonator adapted to produce damped oscillations of a frequency in audible range, a generator producing undamped oscillations of a fre quency in audible range, means to excite said resonator in regular sequence by said generator to produce successive damped oscillation trains of said resonator, the frequency of said oscillation trains being determined by the frequency of said generator, and further means for periodically varying the natural frequency of said resonator,

9. In an electrical musical instrument, a gem erator for producing electric relaxation oscillations defining by their frequency the pitch of the tone, said generator comprising a source of current, a gaseous discharge device containing a heated cathode and an anode, a condenser and an impedance connected therewith, whereby said condenser becomes periodically charged and dip charged, an auxiliary electrode for said discharge device, and means for impressing an auxiliary potential thereon.

10. In an electrical musical instrument, a gen erator producing electrical oscillations adapted to define by their frequency the pitch or the tone, a progressively adjustable resistance for controlling said frequency, said adjustable resistance comdischarge device adapted to produce relaxation oscillations, and a coupling between said generator and said electric discharge device, said coupling being adapted for transferring a small portion of the voltage of said generator to the circuit of saidelectric discharge device, whereby the ignition of said discharge device is synchronized with the frequency of said generator.

12. In an electric musical instrument, a generator producing electrical oscillations defining by their frequency the pitch of the tone, an electric discharge device adapted to produce relaxation oscillations, and a coupling between said generator and said electric discharge device, said coupling being adapted for transferring a small portion of the voltage of said generator to the circuit of said electric discharge device, whereby the ignition of said discharge device is synchronized with the frequency of said generator, said generator consisting of an electric discharge device of the same kind as said discharge device for producing relaxation oscillations, each of said discharge devices containing a control electrode defining by its electric'potential the oscillation frequency, and a common adjusting device for this potential.

13. In an electric musical instrument, a loud speaker, a generator producing electrical oscillations determining the pitch of tone, a play-board for controlling the pitch of tone by depressing a corresponding point of said play-board, a starting contact connected to said play-board, said starting contact including a rheostat adapted to steadily decrease its resistance value from infinite to a predetermined minimum value by slight actuating pressure, and a separate regulator for adjusting the sound intensity from a minimum through a medium to a maximum value, said rheostat controlling the passage of the electrical oscillations to said loud speaker and the minimum value of said rheostat being substantially lower than the medium resistance value of the said adjustable regulator. I

14. In an electrical musical instrument as claimed in claim 13, including means for producing the electrical oscillations prior to the passage of said oscillations through said rheostat.

15. In an electrical musical instrument as claimed in claim 13, including a separate controlling device for adjusting the sound intensity, the adjustment of said controlling device being independent from the pressure exerted to said play-board for forming the pitch of tone.

16. In an electrical musical instrument as claimed inclaim 13, said play-board comprising means for producing in said generator electrical oscillations of a frequency intermediate between the highest and lowest pitch of tone of said playboard when the play-board is not actuated without causing passage of these intermediate oscillations to the loud speaker.

17. In an electrical musical instrument as claimed in claim 13, a switch mechanically coupled to said starting contact, and actuating a retardation device adapted to cause the amplification to slowly fade out.

FRIEDRICH TRAUTWEIN. 

